Definitely one of the worst. Has about the same coverage as a tinted primer, doesn't build at all, is lumpy and unblendable. I'm actually convinced this is meant to be used as a primer to the powder mineral foundation, except you could definitely get better primers than this as this is oddly textured.
As others have said; you cannot, with any method, build this foundation. Not only does it take it completely off but it also turns the foundation beneath into an opaque goo that cannot be smoothed out but instead clumps and pills. If you want to use a lot, which is is necessary as there is very little coverage, you have to swipe it on in one go. Can't use a brush or beauty blender due to textural and buildability issues. It's lumpy even on the back of the hand - this wouldn't bother me if it applied well, but it doesn't and is demonstrative of the issues to come.
It won't cover redness or unevenness, nor mask pores. Not to any degree. If you have very near perfect skin and want it to look like you aren't wearing anything (I mean like... you need to fool your own mother type of stealth) then this does so little in terms of coverage that it'd probably work (permitting you work around the other issues). There have been times i've put this on and legitimately felt I looked better with bare skin. Others, when pulling out all the stops to make it work, I felt like it did enhance, but not enough to measure to any of the other foundations I own. It doesn't look any more subtle than those either.
I will say that the shade was great though. It's hard to tell with so little coverage when wearing, but looking at it before it's blended away it looks very youthful, neutral and brightening in colour. Other companies have wider shade ranges, but given it's sheer and neutral I think most people could find a shade. For reference, I had the lightest shade, and am #13 in Korean foundations (maybe NC/NW 10??). The packaging was also very nice.
I'd recommend the company to fix the balling problem and market this as a coverage enhancing primer for their powder. Used sparingly as a primer without building, maybe I wouldn't be so disappointed. It has a gel texture which I think would likely enhance powder foundations. Even still, there's better in the market at cheaper prices. Sorry, but I wish I didn't spend $40 on this.